Corticosteroids are among the most used and misused medications in veterinary medicine. They exert a powerful, reliable, and
rapid effect, and there is no viable, more effective therapeutic alternative in animals with certain skin conditions. Topical
and oral corticosteroid therapies are considered the first choice for treatment of acute and chronic inflammatory skin diseases,
particularly allergic dermatitis. In addition, they aid in the inflammation associated with some types of infections, primarily
Malassezia dermatitis and otitis.
Using oral corticosteroids
As a review, the oral corticosteroids available for dogs are listed in Table 1 along with their relative potencies, half-life, and relative mineralocorticoid effects. As you can see from the table, these
drugs' half-life becomes much longer as the potency increases. This is important from a clinical standpoint because many patients
that are treated for more than two to three weeks with oral corticosteroids experience side effects.1 To minimize these effects, clinicians should use an alternate-day protocol when administering oral corticosteroids longer
than two weeks.
Table 1. Oral Corticosteroids Used in Dogs
The incidence of side effects—either annoying or more serious—increases as the potency of the corticosteroid increases. Some
controversy surrounds the use of oral triamcinolone in regard to its potency and half-life. To be conservative, it is best
to assume that oral triamcinolone has a greater potency than prednisone or prednisolone and has a longer biologic half-life—closer
to 36 hours. Therefore, practitioners should reserve the use of oral triamcinolone in dogs for treatment of serious refractory
skin diseases. Oral dexamethasone should be used in canine cases only if no other treatment has been successful and the owners
have been warned about the potential serious side effects, or the owners are debating the pet's quality of life (i.e., they are considering euthanasia).
The mineralocorticoid effects of corticosteroids are responsible for increased water consumption, subsequent increased urine
output, and potential urinary incontinence. Prednisone and prednisolone exert a slightly stronger mineralocorticoid effect
than methylprednisolone. Therefore, methylprednisolone may be used instead of prednisone or prednisolone in cases of undesirable
increases in water consumption and urine output.
The most commonly administered oral corticosteroids are prednisone and prednisolone, the latter being more effective in cats.
In dogs, a short regimen of prednisone or prednisolone usually results in mild to no side effects.
Most clinicians in private practice are regularly faced with challenging dermatologic cases, and a common question arises:
How much prednisone is too much? No one can definitively answer this question, as different dogs respond in different ways.
Some patients are unaffected by long-term prednisone administration, while others immediately demonstrate polyphagia, polydipsia
and polyuria, or incontinence. Still others show signs of iatrogenic Cushing's disease—muscle wasting, a pot-bellied appearance,
and muscle weakness—early on in therapy. The best approach is to try the safest treatment first, monitor the patient's response
carefully, and adjust the therapeutic protocol if side effects become problematic or the condition does not respond.
Many dogs receiving corticosteroids will experience alterations in blood work, including variable increases in alkaline phosphatase
activity; stress leukograms characterized by neutrophilia, lymphopenia, and eosinopenia; hyperglycemia; hypercholesterolemia;
and occasionally a blunted cortisol response to adrenocorticotropic hormone (ACTH) administration.2 These changes are generally acceptable as they are rarely of clinical importance.
Other side effects commonly seen with long-term therapy include weight gain, a pot-bellied appearance associated with fat
redistribution, alopecia (some hairs fracture, but most are arrested in the telogen phase), thin and poorly elastic skin,
comedones, pustules, and secondary bacterial infections primarily involving the skin and the urinary tract. In one study,
more than one-third of dogs experienced a urinary tract infection when treated with corticosteroids for longer than six months.3